The Deep-sea Drilling Vessel Chikyu, operated by the Japan Agency for Marine-Earth Science and Technology (hereafter JAMSTEC; Mr. Yasuhiro Kato, President) returned to Hachinohe port on October 26 after completing 82days of System Integration Tests (SIT) and operational training starting on August 6, 2006. The following comprises a brief report of SIT results.
1. Details of major test items
(1) System integration tests
The projected objectives were achieved for 5 items (*1) of System integration tests, some challenges for the future remains however. Especially, it is the great achievement that the series of operation for Riser Drilling was conducted successfully (Installation of Blow-out Preventer (BOP) (Photo-1), disconnection / reconnection of Riser Pipes and BOP, performance of Mud Circulation System, etc.) In addition, those performances were conducted successfully at water depths greater than 1,000 meters. When encountered the storm with a wind of over 30 meter/second for the long time, Dynamic Positioning System gave the good performance. The Chikyu's basic performances as the Deep-sea Scientific Drilling Vessel were now convinced.
Because of the bad weather and other factors, some operation schedule had to be changed so that some tasks remains. These tasks are planning to be tested before the Chikyu will commence the expedition for Integrated Ocean Drilling Program in September 2007.
*1 System integration tests (SIT)
1. Running the riser and blow-out preventer (BOP) (Photo-2)
2. Testing the emergency disconnect sequence (EDS) for the riser and BOP
3. Inserting the casing pipe and cementing
4. Test operation of the Chikyu's three core sampling systems
5. Testing the wireline logging system (which measures formation properties.)
(2) Drilling operation plan
The test drilling off the Shimokita Peninsula was scheduled for completion by October, as the weather typically begins to worsen in November in this area of northeastern Japan. But the severe weather of Typhoon No.12, 13, 14 and rapidly developed low-pressure (Photo-3) during the test period interrupted the operation and made them stand-by.
On October 7, BOP Hydraulic Connectors had damages during weather-related emergency disconnection of Riser Pipes and the upper BOP (LMRP) from the lower BOP. A malfunction of the cuttings transfer mechanism was found in the mud disposal unit. Due to these reasons, the work schedules delayed from the initial projection. Therefore, the targeted drilling depth could not be achieved.
However, as mentioned above, the projected overall objectives were achieved for System integration tests and drilling operations, including the riser drilling, were conducted up to 647m below the sea floor.
(3) Scientific significance of the core samples
During this test drilling, the Chikyu succeeded to collect core sample of 365 meters long (Photo-4). The core sample that had been collected from the bottom of the hole was estimated to be of 650,000 years ago based on the identification of several tephras and microfossils in the core. The core mainly composed of clayey sediments that include many marine planktonic fossils and volcanic-clastics.
It could be possible to determine the core's precise age and estimate the past climate change in Tohoku region from the analysis of wide range of volcanic ash (tephra) layers (for example; we identified a volcanic ash layer at about 600m below the sea floor is Mt. Aso of Kyushu origin, approx.90,000 years ago)
2. Future schedules
The Chikyu will leave Hachinohe port after loading equipments for the overseas drilling shakedown (*2), head to the next test drilling site, off Kenya, and plan to arrive the site at the end of November.
The malfunction of the cuttings transfer mechanism and the damages on BOP Hydraulic Connectors will be fixed during the period from Hachinohe departure to the completion of overseas drilling shakedown.
Details of the test drilling off the Shimokita Peninsula which was the first test drilling for the Chikyu will be evaluated thoroughly. Operation standards will be reviewed as needed based on the experiences from this test drilling including the malfunction and damages caused to equipments and also from upcoming overseas drilling shakedown. Therefore, the launch of the Chikyu's international operations for the Integrated Ocean Drilling Program at the sea of Kumano of the Nankai Trough in September 2007 will be fully prepared.
*2 The overseas drilling shakedown
During the operational test period, before the launch of the Chikyu's international operations, JAMSTEC will carry out a drilling contract at off Kenya and off Australia received from Woodside Energy Ltd., an Australian resource developer, through the Norwegian drilling contractor Seadrill Offshore AS. The aims of this contract are to have sufficient drilling operation experience and to develop deep-sea scientific drilling technologies and transfer those technologies to Japan.